The Shocking Truth Behind Boat Electrical Systems and Batteries
April 27, 2025 | Boat maintenance
Submerged and Damaged: A Cautionary Tale
As I embarked on the conversion of my river boat to an electric engine in the spring of 2022, I couldn’t help but wonder about the potential risks of submerging the electrical system and batteries. Would the batteries explode, or would the system remain intact? I was about to find out the hard way. On a drizzly Sunday in October 2023, I received a call from the harbour patrol, alerting me to a crisis. My boat, Swift, had settled onto her mooring weight, punching a hole in the underside. The lowest tide of the year had left her exposed to the elements, and the consequences were devastating.
Electrolytic Corrosion: A Silent Killer
As I waded into the boat to assess the damage, I noticed that the power cables were severely damaged by electrolytic corrosion. The main 150A fuse and fuse holder were fried, and the batteries appeared intact, but one felt warm. It was then that I realized the true extent of the damage. The batteries, containing 5kWh of power, had been exposed to seawater, which had seeped into the battery casing, causing a complete mess. The design oversight was glaringly obvious: the battery casing was not watertight. Every other part of the electrical system that had been submerged was also damaged, including the power electronics in the engine controller.
A Lesson Learned
The incident served as a stark reminder of the importance of designing electrical systems and batteries with water ingress in mind. The manufacturer’s failure to provide a watertight battery casing was a design oversight that could have catastrophic consequences.
A Journey to Repair
I was devastated, but I knew I had to act quickly to prevent further damage. I commissioned a master clinker boatbuilder, Marcus Lewis, to repair the hole and replace the damaged components. The electric motor went to specialists CPMR in St Austell, who baked dry, fitted with new bearings, and tested before returning a few days later for less than £200. I also replaced the damaged batteries with new ones, selecting Ecoworthy 100Ah batteries, priced less than half that of the originals. The new items cost about £2,000, but the end result was worth it.
A Fully Revived Swift
When the controller arrived, it wouldn’t work, and detailed communication was required to figure out it had the wrong firmware revision. I was sent another unit, but returning the first was a hassle in the post-Brexit world of import/export paperwork. However, with the help of the manufacturer, I was able to get the system up and running again. The fully revived Swift was back on the water for the 2024 season, performing perfectly throughout. She made the trip to a festival in Looe, completing the 11-mile journey with nearly 40% battery remaining. She continues to turn heads with her old-fashioned lines contrasting with high-tech solar panels, and amazes people with her near-silent motoring.
The incident serves as a cautionary tale for boat owners and builders. It highlights the importance of designing electrical systems and batteries with water ingress in mind. The consequences of neglecting this aspect can be severe, and the cost of repairs can be substantial. As I reflect on the experience, I realize that it was a valuable lesson learned. The conversion to an electric engine had been a success, but it had also exposed a vulnerability in the system. By taking the necessary precautions and investing in the right components, I was able to prevent further damage and get the system up and running again.
If you’re considering converting your boat to an electric engine, take heed of this cautionary tale. Make sure to design your electrical system with water ingress in mind, and invest in high-quality components that can withstand the elements. Don’t be afraid to ask for help and advice from experts, and always be prepared for the unexpected.
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